Recently, a variable valve device is proposed in which valve timings of intake or exhaust valve are controlled by transmitting rotative force of an electric motor through a speed-reduction mechanism to a cam shaft (output shaft) and thereby varying a relative rotational phase of the cam shaft to a sprocket to which rotative force is transmitted from a crankshaft.
For example, a variable valve device disclosed in Patent Literature 1 includes an eccentric shaft which receives rotative force of an electric motor, an internal-teeth constituting portion which is formed in a radially-inner portion of sprocket and formed with internal teeth, and a plurality of rollers which are provided between the internal teeth and the eccentric shaft and have total number smaller than total number of the internal teeth. This variable valve device employs a speed-reduction mechanism configured to output rotative force from a retainer that restricts a circumferential movement of the plurality of rollers.